Method of measuring the turbidity of gas-containing liquid mediums with microorganisms

ABSTRACT

From a vessel in which micro-organisms grow in a liquid medium containing gas bubbles, a sample is withdrawn into an exterior measuring chamber by means of suction. Gas bubbles are allowed to escape from the sample and thereafter the opacity or turbidity of the sample is measured by passing a light beam through it.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 559,156 filedMarch 17, 1975 (now U.S. Pat. No. 3,962,041).

BACKGROUND OF THE INVENTION

The present invention relates generally to the measurement of fluidopacity, and in particular to measuring the turbidity of a fluid inwhich micro-organisms are growing, for the purpose of monitoring thegrowth of these organisms.

Still more specifically, the invention relates to a method of carryingout such measurements and to an apparatus for carrying the method intoeffect.

When micro-organisms are grown in a vessel, for example a so-called"fermentor", their development must be monitored from time to time. Thisis done by testing the turbidity of the liquid nutrient medium in whichthey are being grown. The measurements can be taken within the vesselitself or a sample can be removed from the vessel to an exteriormeasuring chamber. In the latter case it is of course necessary toprovide pumps which withdraw the sample and return it subsequently tothe vessel, and pumps, the conduits and the separate measuring chambermust be frequently and separately sterilized, i.e. they must besterilized independently of any sterilization that may be carried out inthe vessel at the end of the production of a batch of micro-organisms.

In all prior-art devices the measuring results have not been as accurateas is desirable. The reason for this is that the micro-organisms requirefor proper growth constant admission of gaseous fluid, such as air oroxygen, into the liquid nutrient medium. This means that the gaseousfluid is present in form of bubbles in the liquid nutrient medium, andwhen a turbidity measurement is carried out, the presence of thesebubbles in the sample of the nutrient medium to be measured tends toadversely affect the accuracy of the measurement. While the problem hasbeen recognized, heretofore no way has been suggested for eliminatinggas bubbles from the sample before the measurement is carried out,because the liquid nutrient media and the micro-organisms containedtherein do not readily lend themselves to a de-gasification prior tocarrying out the measurements.

SUMMARY OF THE INVENTION

It is a general object of the present invention to overcome thedisadvantages of the prior art.

More particularly it is an object of the present invention to provide animproved method and apparatus for measuring the turbidity of a liquidwhich contains a gaseous phase.

Another object of the invention is to provide a method and apparatus ofthis type which permits a photoelectric measurement of the turbidity tobe carried out.

An additional object of the invention is to provide such a method andapparatus which does not require outside conduits that present problemsin sterilization.

In keeping with these objects and with others which will become apparenthereafter, one feature of the invention resides in a method of measuringthe opacity of fluids, particularly of monitoring the growth ofmicro-organisms suspended in a gas-containing liquid medium, bymeasuring turbidity. The method comprises the steps of drawing a sampleof the medium from a vessel into an external measuring chamber,measuring the turbidity of the sample after gas bubbles in the samplehave escaped from it, and reintroducing the sample from the measuringchamber into the vessel.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE illustrates a simplified view of an apparatus forcarrying out the present method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference numeral 2 identifies the wall of a vessel (e.g. a fermentor)which contains liquid nutrient medium wherein micro-organisms are beinggrown and a gaseous phase, present in form of bubbles in the nutrientmedium. The growth of the micro-organisms in this liquid-gas content ofthe vessel 2 is to be measured, for which purpose the turbidity of thecontents is to be determined.

According to the present invention an arrangement is provided which ismounted on the wall 2 by means of screw threads 1 and which has ameasuring tube 3, a measuring chamber 4 wherein the de-gasification ofthe sample is to take place, and a movable bellows 5 (which could bereplaced by a diaphragm) that is mounted in the chamber 4. The bellows 5or the could both be of synthetic plastic material, for instance ofpolyvinylchloride or the like. A piston rod 6 is provided and is coupledwith a drive 7, for instance an electric motor. It is connected with apiston 8 having a lower end portion 9 of reduced diameter. The piston 8is dimensioned to enter into the opening of the measuring tube 3 and thereduced diameter end portion 9 is dimensioned to enter into an opening10 at opposite sides of which two lenses of Pyrex or quartz glass 11 areprovided. The lower end of the end portion 9 carries a wiper plate orround glass 12, e.g., of nylon or the like synthetic plastic that isflexible.

Arranged at the left-hand side of the device is a light source 13 whichdirects a beam of light across the gap 10 through the two lenses 11,which beam is then received by a photoelectric cell 14 located at theright-hand side, wherein it produces a current whose magnitude dependsupon the magnitude of the light beam, and which is amplified at anamplifier 15. A plurality of seals 16, four in the illustratedembodiment, is provided to seal the arrangement with respect to thesample to be measured.

To carry out the method according to the present invention, a sample ofthe gas-containing liquid nutrient medium is withdrawn from the interiorof the vessel 2, by making the piston rod 6 and the piston 8, 9 performa suction stroke after it has first been moved forwardly (downwardly inthe drawing). The resulting expansion of the previously compressedbellows 5, which should preferably be of a heat-resistant syntheticplastic material, causes a sample of the liquid nutrient medium with themicro-organisms and gas bubbles to be drawn via the measuring tube 3into the degassing chamber 4. In the chamber 4 the sample is allowed torest for a period of time which is to be determined empirically untilthe gas bubbles in the liquid have escaped upwardly and left the liquidnutrient medium. The determination of the period of time required forthis is very simple and requires no undue experimentation.

After the gas bubbles have so escaped, a light beam is directed acrossthe gap 10 from the light source 14, and when it impinges upon thephotoelectric cell 14 it produces a current which is amplified in theamplifier 15 and can then be used to provide the desired information,e.g. to operate a scriber or the like. The magnitude of this currentdepends upon the intensity of the light beam which travels across thegap 10, and the intensity of the light beam in turn is influenced by theturbidity of the liquid, so that the intensity of the light beam and themagnitude of the current provides an indication of the growth ofmicro-organisms since these influence the turbidity of the liquid.

After the measurement is completed, the piston 8 is moved downwardlyinto the measuring tube 3, thereby ejecting the sample back into thevessel 2. During this movement the wiper disc 12 wipes over the lenses11 and cleans the same. The chamber is now ready for a new measurementto be taken.

When the development of micro-organisms in the contents of the vessel 2is complete, the contents are removed. Before a new batch of materialcan be admitted into the vessel, the latter must be sterilized to avoidcontamination of the material. This can be carried out in theconventional manner, for example by means of steam, and since there is adirect communication between the vessel and the arrangement according tothe present invention, through the gap 10, sterilization of the vessel 2will at the same time also result in sterilization of the arrangementaccording to the present invention.

Thus, the disadvantages of the prior art are eliminated, since nocomplicated equipment is provided which is difficult to sterilize, andsince it is now possible to measure the turbidity of the liquid withoutthe presence of the gas bubbles which have deliterious effect on themeasurements taken.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inmeasuring the turbidity of a liquid in which micro-organisms aregrowing, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A method of measuring the turbidityof gas-containing liquid mediums with microorganisms, comprising thesteps of establishing a fluid-communication path between a vessel and ameasuring chamber; drawing a sample of the medium from said vessel intosaid measuring chamber; measuring the turbidity of the drawn sampleoutside said vessel after gas bubbles in the drawn sample have escapedfrom it; thereafter reintroducing the drawn sample from said measuringchamber into said vessel; and thereafter sterilizing said vessel, saidpath and said measuring chamber simultaneously and together prior tointroduction of the new medium into the vessel and without interruptionof said paths.
 2. A method as defined in claim 1, wherein the step ofdrawing comprises the application of suction to withdraw the sample fromthe vessel.